Method for the preparation of alpha, alpha, alpha&#39;, alpha&#39; -tetrachloro-p-xylene with high purity

ABSTRACT

A method of synthesizing a high purity product of α, α, α′, α′-tetrachloro-p-xylene is disclosed. The method includes carrying out a first stage reaction of terephthaldicarboxaldehyde with a mixture of SOCl 2  and dimethylformamide (DMF) to obtain a product mixture containing α, α, α′, α′-tetrachloro-p-xylene as a major product and 4-dichloromethyl benzaldehyde as a side product; adding SOCl 2  and DMF to the product mixture of the first stage reaction to undergo a second stage reaction; and to a cool water adding the resulting product mixture from the second stage reaction to obtain a solid product of α, α, α′, α′-tetrachloro-p-xylene with a purity of 90-99 mol %.

FIELD OF THE INVENTION

The present invention relates to a novel method for synthesizingα,α,α′,α′-tetrachloro-p-xylene, particularly a method for synthesizingα,α,α′,α′-tetrachloro-p-xylene by reacting terephthaldicarboxaldehydewith a mixture of SOCl₂ and dimethylformamide (DMF).

BACKGROUND OF THE INVENTION

Dolbier, William R., Jr.; Rong, Xiao X.; Stalzer, Walter E. et. al. inWO 98/24743 (1998) proposes a method for synthesizingα,α,α′,α′-tetrafluoro-p-xylene by a replacement reaction ofα,α,α′,α′-tetrachloro-p-xylene.

The following introduces methods for synthesizingα,α,α′,α′-tetrachloro-p-xylene published in the prior art.

U.S. Pat. No. 4,328,374 (1982); U.S. Pat. No. 4,465,865 (1984); JP51006931 (1976); JP560123329 (1981); EP 54634 (1982) and WO 98/24743(1998) disclose a method for reacting p-xylene with chlorine by aphotochlorination reaction according to the following reaction formula:

The abovementioned method needs to use a photoillumination device andthe reaction is very difficult to be controlled to form a chlorinatedproduct having just four chlorine substituents. Instead a productmixture containing three or less or five or more chlorine substituentswill be produced, and pure products are difficult to be separated fromthe product mixture due to their similar polarities. For example, thephotochlorination reaction disclosed in WO 98/24743 (1998) has areaction time of 110 hours and a yield lower than 35%. Furthermore, theproduct mixture contains not only a chlorinated product having fourchlorine substituens, but also incomplete and over-reacted productshaving less than three chlorine atoms and over five chlorine atoms. Theproduct mixture is difficult to be purified.

Mikhailov, V. S.; Matyushecheva, G. I.; Yagupol'shii, L. M.; Zh. Org.Khim., 9(9), 1824 (1973) propose a method for preparingα,α,α′,α′-tetrachloro-p-xylene by reacting p-xylene with phosphoruspentachloride (PCl₅). Such a method has the following reaction formula:

The α,α,α′,α′-tetrachloro-p-xylene product in the abovementionedreaction has a yield of 17-35% and is difficult to be separated.

JP79125629 (1979) discloses a method for preparingα,α,α′,α′-tetrachloro-p-xylene by reacting 4-methyl benzaldehyde withPCl₅, forming an intermediate product 4-methyl,1-(dichloromethyl)benzene, and conducting a photochlorination reaction.This prior art method has the following reaction formula:

The abovementioned reaction is a two-step reaction. Even though thefirst step reaction has a yield of 96.5%, the second step reaction has avery low yield. The product mixture is very difficult to be purified.

George W. Kabalka; Zhongzhi Wu, Tetrahedron Lett. 2000, 41, 579-581 havepublished a method for preparing α,α,α′,α′-tetrachloro-p-xylene byreacting terephthaldicarboxaldehyde with BCl₃. This published method hasthe following reaction formula:

The abovementioned reaction has a yield reaching 98%. However, BC13itself is a gas which makes it difficult in transportation. 1.0M BCl₃ inhexane has a large volume due to its low concentration, which makes thesolution difficult in transportation and is not convenient in massproduction.

SOCl₂ and a catalytic amount of DMF can be used in the production ofchlorinated benzaldehyde or a benzaldehyde compound having a substituenton the phenyl ring thereof. For example, Melvin S. Newman, P. K.Sujeeth, J. Org. Chem., 43(22), 4367, 1978 has proposed thatα,α-dichlorotoluene can be produced by reacting SOCl₂/DMF withbenzaldehyde.

SUMMARY OF INVENTION

The present invention provides a new synthesis method by reactingterephthaldicarboxaldehyde with SOCl₂/DMF to obtainα,α,α′,α′-tetrachloro-p-xylene and about 10-20 mole % of4-dichloromethyl benzaldehyde as a by-product. Because the reactantterephthaldicarboxaldehyde itself is solid, it is difficult to be mixedwith SOCl₂ without the presence of a solvent. Therefore, said reactioncan be conducted in a solvent (e.g. DMF) non-detrimental to the reactionand a temperature of 70-95° C. in order to solve the mixing problem.Compared to BCl₃, the chlorination agent SOCl₂ of the invented methodhas the following advantages: cheaper, smaller volume, convenient intransportation. The method of the present invention also has a higheryield, shorter reaction time and lower reaction temperature incomparison with the photochlorination reaction. The main product and theby-product 4-dichloromethyl benzaldehyde in the product mixtureaccording to the present invention have a great difference in polarity.Therefore, the separation/purification of said main product is easy. Thepresent invention also discloses a method for further reducing thecontent of the by-product 4-dichloromethyl benzaldehyde to lower than 2mole %, which comprises adding SOCl₂/DMF batchwise intoterephthaldicarboxaldehyde in the reaction of terephthaldicarboxaldehydewith SOCl₂/DMF.

DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses a novel method for synthesizingα,α,α′,α′-tetrachloro-p-xylene by reacting terephthaldicarboxaldehydewith a mixture of SOCl₂ and dimethylformamide (DMF).

In the method of the present invention, the molar amount of SOCl₂ usedis 0.1-10 times, preferably 2-3 times, of that ofterephthaldicarboxaldehyde used.

In the method of the present invention, the amount of DMF used is 1-100g, preferably 5-25 g, per mole of terephthaldicarboxaldehyde.

In the method of the present invention, the reaction temperature is0-150° C., preferably 70-95° C.

Preferably, the invented method further comprises contacting theresulting product mixture from the reaction with water so that a solidprecipitate is formed; removing the solid precipitate from the mixture;introducing said solid precipitate into a silica column and eluting thecolumn with a non-polar solvent; collecting the eluate resulting fromthe elution; and removing the non-polar solvent contained in the eluateto obtain a α,α,α′,α′-tetrachloro-p-xylene solid.

The present invention also provides a method for synthesizingα,α,α′,α′-tetrachloro-p-xylene with a high purity, which comprises:performing a first stage reaction by reacting terephthaldicarboxaldehydewith a mixture of SOCl₂ and dimethylformamide (DMF) to obtain a productmixture including α,α,α′,α′-tetrachloro-p-xylene as a major portion and4-dichloromethyl benzaldehyde by-product; performing a second stagereaction by adding SOCl₂ and DMF into said product mixture; andcontacting the resulting product mixture from the second stage reactionwith a cooling water to obtain a solid product ofα,α,α′,α′-tetrachloro-p-xylene with a purity of 90-99 mole %.

Preferably, said method for synthesizing α,α,α′,α′-tetrachloro-p-xylenehaving a high purity further comprise: heating and stirring theresulting solid-liquid mixture from said contact to form a dispersion;removing the resulting fine particles of said solid product from saiddispersion and drying the fine particles to obtain anα,α,α′,α′-tetrachloro-p-xylene powder having a purity higher than thatof said solid product. More preferably, said method further comprisescarrying out a third stage reaction by reacting saidα,α,α′,α′-tetrachloro-p-xylene powder with a mixture containing SOCl₂and DMF; contacting the resulting product mixture from the third stagereaction with water to form a solid precipitate; removing the solidprecipitate from the solid-liquid mixture resulting from said contact;and drying the obtained solid precipitate to obtain aα,α,α′,α′-tetrachloro-p-xylene having an even higher purity.

In the abovementioned first stage reaction, the amount of SOCl₂ used is0.1-10 times, preferably 1.5-3 times, of that ofterephthaldicarboxaldehyde used in mole.

In the abovementioned first stage reaction, the amount of DMF used is1-100 g, preferably 5-25 g, per mole of terephthaldicarboxaldehyde.

Preferably, the amount of SOCl₂ used is the same for the first andsecond stage reactions.

Preferably, the amount of DMF used is the same for the first and secondstage reactions.

Preferably, the amount of SOCl₂ used in the third stage reaction islower than that used in the first stage reaction.

Preferably, the amount of DMF used in the third stage reaction is lowerthan that used in the first stage reaction.

Preferably, the first, second and third stage reactions areindependently carried out at a temperature of 0-150° C., preferably70-95° C.

The present invention can be further elaborated by the followingexamples which are for illustrative purposes only and not for limitingthe scope of the present invention.

EXAMPLE 1

35 g (0.26 mol) of terephthaldicarboxaldehyde and 1.7 g of DMF wereloaded in a 100 ml round-bottomed flask, and heated with an oil bath at70° C. 80 g (0.67 mol) of SOCl₂ was slowly added for a period of 30minutes. Upon the completion of the addition, the temperature of the oilbath was increased to 95° C. for 3 hours. Upon completion of thereaction, the product mixture was poured into 500 ml of ice water, and asolid product was formed therein. Next, the solid product was filteredout, washed with 100 ml of ice water three times, and dried in vacuo at70° C./3 mmHg for three hours. After drying, the crude product waspurified by a silica column chromatography, wherein the eluent used inthe first stage eluting was n-hexane, and the eluent used in the secondstage eluting was a mixture of n-hexane and acetic acetate (20:1). Theeluate collected from the first stage eluting was concentrated byevaporation of the organic solvents to obtain 48.5 g (0.20 mol) ofα,α,α′,α′-tetrachloro-p-xylene with a yield of 77%. The eluate collectedfrom the second stage separation was concentrated by evaporation toobtain 9.0 g (0.048 mol) of 4-dichloromethyl benzaldehyde with a yieldof 18.0%. The results of their analysis are:α,α,α′,α′-tetrachloro-p-xylene

-   melting point: 96° C.-   ¹H-NMR(CDCl₃)δ:    -   6.79(2H, s, —CCl₂H)    -   7.70(4H, s, -Ph)-   MS: m/z 244(M⁺)-   4-dichloromethyl benzaldehyde-   melting point: 64° C.-   ¹H-NMR(CDCl₃) δ:    -   6.81(1H, s, —CCl₂H)    -   7.75(2H, d, -Ph)    -   7.97(2H, d, -Ph)    -   10.1(1H, s, —CHO)-   IR(KBr): 1680 cm⁻¹-   MS: m/z 189(M⁺)

EXAMPLE 2

35 g (0.26 mol) of terephthaldicarboxaldehyde and 1.7 g of DMF wereloaded in a 100 ml round-bottomed flask, and then 80 g (0.67 mol) ofSOCl₂ was added. The solution was heated with an oil bath at 95° C. for3 hours. Upon completion of the reaction, the product mixture was pouredinto 500 ml of ice water, and a solid product was formed therein. Next,the solid product was filtered out, washed with 100 ml of ice waterthree times, and dried in vacuo at 70° C./3 mmHg for three hours. Afterdrying, the crude product was purified by a silica columnchromatography, wherein the eluent used in the first stage eluting wasn-hexane, and the eluent used in the second stage eluting was a mixtureof n-hexane and acetic acetate (20:1). The eluate collected from thefirst stage eluting was concentrated by evaporation to obtain 51.65 g(0.21 mol) of α,α,α′,α′-tetrachloro-p-xylene with a yield of 81%. Theeluate collected from the second stage eluting was concentrated byevaporation to obtain 8.4 g (0.045 mol) of 4-dichloromethyl benzaldehydewith a yield of 17.3%.

EXAMPLE 3

1000 g (7.46 mol) of terephthaldicarboxaldehyde were loaded in a 5 literround-bottomed flask and, in a nitrogen environment, 1776 g (1090 ml,14.92 mol) of SOCl₂ and 157.2 g (2.15 mol) of DMF were added. Thesolution was heated, under a mechanical agitation, with an oil bath at70° C. for 1 hour. The resulting mixture was added with 1776 g (1090 ml,14.92 mol) SOCl₂ and 157.2 g (2.15 mol) DMF, and heated under amechanical stirring at 70° C. for 1 hour. Next, the hot reaction productmixture was poured into ice water while stirring to form a solid-liquidmixture. The solid-liquid mixture was indirectly heated with a boilingwater bath under vigorous stirring to form a dispersion, wherein fineparticles of the solid product were well dispersed in the liquid. Theboiling water bath was removed so that the dispersion was slowly cooledto room temperature. The solid in the dispersion was filtered out anddried to obtain a product weighing 1710 g in the form of powder. Theproduct powder contains 94% of α,α,α′,α′-tetrachloro-p-xylene and 6% of4-dichloromethyl benzaldehyde.

120 g of the abovementioned powder product was loaded in a 250 mlround-bottomed flask. In a nitrogen environment, 30 ml of SOCl₂ and 4 mlof DMF were added into the flask, and the resulting mixture was heatedat 80° C. for 2 hours. The hot reaction product mixture was poured intoice water while stirring to form a solid-liquid mixture. Thesolid-liquid mixture was indirectly heated with a boiling water bathunder vigorous stirring to form a dispersion. The boiling water bath wasremoved so that the dispersion was slowly cooled to room temperature.The solid in the dispersion was filtered out and dried to obtain aproduct weighing 122 g in the form of powder having anα,α,α′,α′-tetrachloro-p-xylene purity of 99.1%.

EXAMPLE 4

14.4 g (0.10 mol) of terephthaldicarboxaldehyde, 1.9 g (2 ml, 0.026 mol)of DMF, and 24.5 g (15 ml, 0.20 mol) SOCl₂ were loaded in a 250 mlround-bottomed flask. The mixture was mixed at 85˜90° C. in a nitrogenenvironment for one hour. Next, 24.5 g (15 ml, 0.20 mol) SOCl₂ and 1.9 g(2 ml, 0.026 mol) DMF were dripped into the mixture, and the reactiontemperature was increased to 90° C. for 2 hours. Next, the hot reactionproduct mixture was poured into 500 ml of ice water while stirring toform a solid-liquid mixture. The solid-liquid mixture was indirectlyheated with a boiling water bath and under vigorous agitation, so that adispersion was formed, wherein fine particles of the solid product werewell dispersed in the liquid. The boiling water bath was removed, andthe dispersion was slowly cooled to room temperature. The solidcontained in the dispersion was removed therefrom by filtration, and wasdried to obtain 23 g (0.094 mol, yield 94%) of a dry product powder ofα,α,α′,α′-tetrachloro-p-xylene having a purity of 98.7%.

1. A method for synthesizing α,α,α′,α′-tetrachloro-p-xylene with a highpurity, which comprises: performing a first stage reaction by reactingterephthaldicarboxaldehyde with a mixture of SOCl₂ and dimethylformamideto obtain a product mixture including α,α,α′,α′-tetrachloro-p-xylene asa major portion and 4-dichloromethyl benzaldehyde by-product; performinga second stage reaction by adding SOCl₂ and DMF into said productmixture; and contacting the resulting product mixture from the secondstage reaction with a cooling water to obtain a solid product ofα,α,α′,α′-tetrachloro-p-xylene with a purity of 90-99 mole %.
 2. Themethod as claimed in claim 1 further comprising heating and stirring theresulting solid-liquid mixture from said contact to form a dispersion;removing the resulting fine particles of said solid product from saiddispersion and drying the fine particles to obtain anα,α,α′,α′-tetrachloro-p-xylene powder having a purity higher than thatof said solid product.
 3. The method as claimed in claim 2 furthercomprising carrying out a third stage reaction by reacting saidα,α,α′,α′-tetrachloro-p-xylene powder with a mixture containing SOCl₂and DMF; contacting the resulting product mixture from the third stagereaction with water to form a solid precipitate; removing the solidprecipitate from the solid-liquid mixture resulting from said contact;and drying the removed solid precipitate to obtain aα,α,α′,α′-tetrachloro-p-xylene having a purity higher that of saidα,α,α′,α′-tetrachloro-p-xylene powder.
 4. The method as claimed in claim1, wherein an amount of SOCl₂ used in the first stage reaction is 1.5-3times of that of terephthaldicarboxaldehyde used in the first stagereaction in mole.
 5. The method as claimed in claim 1, wherein an amountof dimethylformamide used in the first stage reaction is 5-25 g per moleof terephthaldicarboxaldehyde used in the first stage reaction.
 6. Themethod as claimed in claim 4, wherein an amount of SOCl₂ used in thesecond stage reaction is the same as in the first stage reaction.
 7. Themethod as claimed in claim 5, wherein an amount of dimethylformamideused in the second stage reaction is the same as in the first stagereaction.
 8. The method as claimed in claim 3, wherein an amount ofSOCl₂ used in the third stage reaction is lower than that used in thefirst stage reaction.
 9. The method as claimed in claim 3, wherein anamount of dimethylformamide used in the third stage reaction is lowerthan that used in the first stage reaction.
 10. The method as claimed inclaim 1, wherein the first and the second stage reactions are performedat a temperature of 70-95° C.
 11. The method as claimed in claim 3,wherein the third stage reaction is performed at a temperature of 70-95°C.